ENTHALPY OF STABILIZATION OF HEN EGG LYSO ZYME STRUCTURE IN DIMETHYLSULFOXIDE AQUEOUS-SOLUTIONS

Scanning microcalorimetry data have been used to plot the dependences of the denaturation enthalpy of hen egg lysozyme on dimethylsulfoxide concentration at fixed temperatures. It has been shown that at dimethy lsulfoxide concentrations below 40% (v/v) the enthalpy does not depend on pH of the medium. An increase of dimethylsulfoxide concentration i n this range leads to a linear growth of enthalpy. The rate of enthalp y growth decreases with the temperature increase. The denaturation ent halpy begins to considerably depend on pH at dimethylsulfoxide concent rations more than 40%. Spectroscopy data indicate that conformational changes occur in the protein in this range of concentrations already a t room temperature, whereas according to scanning microcalorimetry, th ey take place at much higher temperatures. This difference is probably due to a decrease of the real temperature of protein melting below ro om temperature and a very inhibited character of the denaturational tr ansition. This results in a decrease of calorimetric enthalpy at acidi c pH owing to Incomplete protein renaturation upon calorimeter cooling to the starting point.